Genesis 17:9-12

9And God said to Abraham, Thou shalt keep my covenant therefore, thou, and thy seed after thee in their generations. 10This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every male among you shall be circumcised. 11And ye shall circumcise the flesh of your foreskin; and it shall be a sign of the covenant between me and you. 12And he that is eight days old shall be circumcised among you, every male in your generations, he that is born in the house, or bought with money of any stranger, who is not of thy seed.1